Safety lock for switches



June 8, 1954 E. R. MOKITRICK 2,680,368

SAFETY LOCK FOR SWITCHES Filed Aug. '7, 1951 INVENTOR. ZZ/War/ I? /V zVzZr/ci Patented June 8, 1954 Edward R. McKitrick, D

Briggs Manufacturin corporation of Michigan etroit, Mich., assignor to g 00.,

Detroit, Mich., a

Application August 7, 1951, Serial No. 240,667

4 Claims.

This invention relates to a safety lock for'electrical switches and more particularly to asafety lock for electrical switches used to control the starting and stopping of the operation of metal stamping presses or other machines and apparatus.

One type of electrical switch commonly used to control the cperation'of metal stamping presses and other machines or apparatus comprises a housing which encloses the electrical contact ele ments of the switch and which provides a mounting for at least two actuators or push button elements for shifting the contact elements to open and close the necessary electrical circuits "for starting or stopping the drive means of the press or machine. In this type of switch, at least one of the buttons must be pressed to start the operation of the press or machine and another of the buttons must be pressed to stop the operation thereof. The start and stop buttons are interlocked, preferably by mechanical means, in such a manner that movement of one button inwardly into a recessed position within the housing automatically results in the other button being moved outwardly to project beyond the surface of the housing in accessible position to be actuated by the machine operator to start or stop the machine, as the case may be. For example, when the press or machine is in operation the start button will be in a depressed position within the housing and a portion of the stop button will project beyond the surface of the housing in position to be moved inwardly to stop the operation of the press or machine. When the stop button is pressed by the machine operator, it will move inwardly to a recessed position within the housing and the start button will be automatically moved outwardly into a position of readiness to be actuated to re-' start the press or machine.

It is an object of the present invention to provide a simple and inexpensive safety device which may be readily attached to the housing of the electrical switch to prevent the movement of the switch push buttons necessary to start the operation of the press or machine. The present invention comprises a means for preventing or blocking outward movement of the stop button when it is recessed within the switch housing, the stop button being in a recessed position when the machine is not operating. Because of the means interlocking the two buttons for correlated movement, when outward move ment of thestop button is prevented or blocked the start button cannot be moved inwardly to close the electricalcircuit necessary to put the machine or press in operation. In its illustrated embodiment, the present invention comprises a plug-like device which may be inserted into the housing when the stop button is in its recessed or machine inoperative position, the device being locked to the housing by key operated means and when so locked effectively blocking any outward movement of the stop button and thereby blocking the inward movement of the start button. As long as the safety device is in blocking position the machine cannot be operated. 'Thus, a repair man after having inserted the safety device in blocking position in the switch and put the key thereto in his pocket may crawl into the machine or apparatus to make any necessary repairs without the danger of someone inadvertently putting the machine or apparatus into operation while he is in a position to be injured by any of its moving parts.

Other features, objects and advantages of this invention herein illustrated will appear in the following description, reference being had to the accompanying drawings forming a part of the specification wherein like reference numerals designate corresponding parts in the several views.

Fig. 1 is a'front elevation of a start-stop switch and illustrating the present invention mounted thereon.

Fig. 2 is a section taken substantially through line 2-2 of Fig. 1 looking in the direction of the arrows.

Fig. 3 is a section taken substantially through line 33 of Fig. 1 looking in the direction of the arrows.

Fig. 4 is a sectional elevation illustrating the inner mechanism of the present invention.

Fig. 5 is a section taken substantially through lined-5 of Fig. 4.

Before explaining in detail the present invention' it is to be understood that'the invention is not limited in its application to the details of construction and arrangements of parts i1- lustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein isfor the purpose of description and not of limitation.

Referring more particularly to the drawings, the electricalswitch .to which the present invention is applied comprises, for illustrative purposes, a meta-leasing or housing it which fits over an inner casing l i made of a dielectric material. The outer and inner casings I and II, respectively, are adapted to be fastened by means of screws l2 as a unit to the frame structure 13 of a stamping press, machine or other apparatus, a suitable rubber insulating gasket I4 being provided to insulate th metal casing I0 from the press or machine frame 13. The front face l5 of the casing ii] is provided with a raised boss [6 having two spaced bores I! and i8 therein. Two push buttons 19 and 20 are slidably mounted within the bores H and [8 respectively. Push buttons [9 and 20 are provided with stems or extensions I90. and 29a respectively, which project through apertures 2| and 22 in the base plate 23 of the inner casing H, the apertures 21 and 22 being in alignment with the bores H and 18 in the outer casing H). A compression spring 24 is seated over each stem la and 20a, each spring being adapted to be compressed between one surface of the base plate 23 and the inner surface of the corresponding push button I9 or 20.

Mounted on the end of each push button stem 19a. and Zfla is a cylindrical brass member 25 having a longitudinally extending slot 26 therein. Pivotally mounted in each slot 26 by means of a cotter pin 27 is a dielectric link 28. Each link 28 is pivotally connected to one end of a cross bar 29 which is pivoted intermediate its ends on a pin 36 carried on one end of a yok member 31 mounted at its other end to the base plate 23 of the inner casing l l.

The foregoing construction and arrangement is such that when one push button is in a depressed position relative to the outer casing H], as for example the push button 29 as shown in Fig. 3, the other push button will have a portion thereof projecting beyond the outer surface of the boss is of the outer casing H1. Movement of the outwardly projecting button in an inward direction automatically results in the cross bar 29 urging the recessed button outwardly into a position of readiness to be actuated when desired by the machine operator.

Suitable contact means in the form of metallic washers 32 are carried on each cylindrical brass member 25. The contact means are urged by compression springs 34 into contact with suitable contact elements 33 carried within the inner casing l I.

It is believed that the foregoing description of the illustrative type of electric switch with which the present invention is adapted to be utilized is of sufficient detail for an understanding of the invention.

The embodiment of the invention illustrated herein comprises a cup-like cylindrical base or plug portion 35 having a diameter substantially equal to the diameter of the stop push button 20 of the electric switch and is thereby readily insertable in the bore 18 of the switch housing ill, in which bore the stop button 2c is mounted. It will be understood that the base or plug portion 35 of the safety device is only insertable in the bore i8 when the stop button is in its recessed position. i. e. the position the stop button occupies after having been pressed to stop the operation of the press or machine. The base or plug portion 35 is held within the bore [8 adjacent the upper surface of the push button 20 preferably by means of radially movable pins 36. At least two pins 35 are journalled in radially extending apertures 3'! in the base or plug portion 35 for movement laterally of the base, the apertures 31 being bored to extend into the central cavity 35a of the plug portion 35. The pins are headed on their inner ends, the heads 38 providing means for retainin compression springs 39 on the pins for urging the pins radially inwardly at all times. The pins are urged radially outwardly by a substantially oval shaped cam 40 carried on the end of a shaft 4!. When the cam 40 is in the position in which its major axis is at a right angle to the common longitudinal axis of the two pins 36, the springs 3S will hold the pins 36 inwardly relative to the base plug portion 35 so that only a small portion of each pin will project beyond the cylindrical surfaces of the base, as shown in Fig. 5. When the cam 49 is rotated to bring its major axis in alignment with th common longitudinal axis of the pins 36, the cam will urge the pins outwardly so that a portion of each pin will project a substantial distance beyond the cylindrical surface of the plug 35.

The shaft 4! for rotating the cam 40 is connected to a conventional key cylinder mechanism 42 operated by the usual key. By turning the key 43 in the key cylinder mechanism the cam 40 may be turned in one direction to move the pins 36 radially outwardly. Reverse turning of the key will of course turn the cam 40 in the opposite direction permitting the springs 39 to retract the pins 35. The key cylinder mechanism may be fastened to the base-or plug portion 35 in any conventional manner. As illustrated in Fig. l, the key cylinder mechanism 42 is shown seated in a counterbored portion 35b of the base portion cavity 350:. Suitable screws 43 extend through the bottom wall of the base cavity 35a into the hey cylinder mechanism 42 to retain the latter in place.

The wall of the switch housing bore i8 is provided with two diametrically opposed longitudinally extending notches 44 of sufficient depth to permit ready passage of the projecting ends of the pins 36 when the latter are in their retracted position relative to the base or plug portion 35. Each notch 154 is intersected a suitable distance below the surface of the switch housing boss 16 by radially aligned apertures 45 bored to penetrate the inner wall of the bore 18 and adapted to receive the pins 36.

When it is desired to prevent the operation of a press or machine for any reason the safety device embodying the present invention is inserted into the bore i8. The projecting ends of the pins 36 will be guided by the notches 44 to ensure that the pins will be properly aligned with the apertures 45 in the bore wall. Upon the key 43 being turned, the cam 4i! will force the pins 35 radially outwardly into the apertures 45 thereby locking the base or plug portion 35 into the bore IS. The key 43 may then be removed and the safety device embodying the present invention will effectively prevent actuation of the switch thereby rendermg the same inoperative to supply electrical power to the press or machine drive means. As has been explained, usually when the start button of the switch is pushed inwardly to close the electrical circuit for putting the machine in operation the stop button is automatically moved outwardly into a position of readiness to be actuated to stop the machine. However, with the safety device embodying the present invention preventing outward movement of the stop button, the start button cannot be moved inwardly.

When it is desired to place the press or machine back in service it is only necessary that the key be inserted in the safety device and turned to rotate the cam 46 in a direction to move the cam surface out of the path of the pins 36. The springs 39 will then cause retraction of the pins 36 and the base or plug portion 35 may be withdrawn from the bore 18 thus unblocking outward movement of the stop button. With the stop button free to move outwardly, the start button may then be actuated to supply the necessary electrical current for operation of the press or machine.

I claim:

1. A safety device for an electrical switch having start and stop push buttons interconnected for shiftable movement in unison and in opposite directions and a support having a cylindrical recess within which the stop button is shiftable inwardly into depressed position whereby the start button is shifted outwardly into operative position, comprising a cylindrical blocking member conforming substantially to the shape of said recess and insertable into said recess in abutting relation to said stop push button when the latter is in depressed position, shiftable locking means carried by said blocking member, and key actuated means for shifting said locking means into position to lock said blocking member within said recess.

2. A safety device for an electrical switch having start and stop push buttons interconnected for shiftable movement in unison and in opposite directions and a support having a cylindrical recess within which the stop button is shiftable inwardly into depressed position whereby the start button is shifted outwardly into operative position, comprising a cylindrical blocking member conforming substantially to the shape of said recess and insertable into said recess in abutting relation to said stop push button when the latter is in depressed position, shiftable looking means carried by said blocking member, said support having keeper means, and key actuated means for shifting said locking means into engagement with said keeper means to lock said blocking member within said recess.

3. A safety device for use in conjunction with an electrical switch having push button actuat- 4 ing elements for correlated movements so that when one button is shifted inwardly into depressed position another button is shifted outwardly into operative position and having a housing support provided with cylindrical recesses within which said elements are shiftable, comprising a cylindrical plug conforming substantially to the shape of one recess and insertable thereinto in abutting relation to the actuating element therein when depressed, movable locking means mounted in said plug adapted to be received in an aperture in the wall of said one recess, means for moving said locking means outwardly of said plug into said aperture to lock the plug in said one recess and block outward movement of said last named actuating element thereby preventing actuation of the other actuating element.

4. In a safety device for an electrical switch having cylindrical start and stop push buttons interconnected for axially shiftable movement in unison and in opposite directions and a support having a cylindrical recess within which the stop button is shiftable axially inward to a depressed position, comprising a cylindrical blocking member conforming substantially to the shape of said recess and removably insertable axially thereinto in abutting relation to said stop button when the latter is in depressed position, said support having a pin hole opening substantially into said recess, a locking pin carried by said member and having an end shiftable into said pin hole when said member is positioned in said recess in blocking position, and key actu-- ated means for shifting said locking pin into said pin hole to lock said blocking member in said blocking position.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,706,518 Blough Mar. 26, 1929 1,749,984 Nogueira Mar. 11, 1930 1,806,307 Norviel May 19, 1931 1,892,192 Smith Dec. 27, 1932 2,484,424 Rosing Oct. 11, 1949 

